I think another aspect of it is that the league is affiliated with a religion (or rather a denomination of a religion) that is kind of known for seeing women as inferior. Apparently this league was willing to overlook it for a while since the girl was having fun, her coach and teammates were supportive and the parents of the other players on the team were cool with it too.
But I guess someone threw a fit because she was just too good and suddenly "Oops, no girls allowed, you can't play anymore!"
There was a girl on my high school's football team. She was very well respected amongst the girls and guys because she was very good. I remember mentioning said girl at home and my father said "Oh, she must be a kicker, that's the only safe football position for a girl."
No, she wasn't a kicker, she was in there tackling like the others.